The present invention relates to a solid state image sensing device, more particularly to a solid state image sensing device with reduced occurrence of smear phenomenon, and also to a method of manufacturing the same.
Generally, in solid state image sensing devices, signal charges corresponding to an image focussed on light receiving surfaces of solid state image sensing elements disposed in a matrix fashion are sampled from photosensitive pixel areas of the solid state image sensing elements, and the sampled signal charges are transferred to charge transfer areas to time-sequentially output image signals to a TV monitor or the like. It is therefore necessary for the charges generated in a semiconductor substrate by photoelectric conversion to be separated for each pixel. Thus, each pixel must be optically separated.
In one example of a conventional solid state image sensing device wherein each pixel is optically separated, a photosensitive pixel area and a charge transfer area are formed on the surface of a semiconductor substrate. A light shielding layer of aluminum Al or aluminum silicide Al-Si is formed above the charge transfer area with an insulating layer interposed therebetween. This device is fabricated in the following manner.
A photosensitive pixel area (not shown) and a charge transfer area (not shown) are formed on the surface of a semiconductor substrate, and thereafter, a transfer electrode of a polysilicon layer is so formed above the charge transfer area that an oxide film formed on the semiconductor substrate through thermal oxidation is interposed between the transfer electrode and the surface of the semiconductor substrate. Further, an oxide film is formed on the transfer electrode through thermal oxidation. Next, an insulating layer is deposited over the entire surface by a chemical vapor deposition (CVD) method and thereafter, phosphorus is diffused into the insulating layer. A light shielding layer of aluminum Al or aluminum silicide Al-Si is formed on the insulating layer above the transfer electrode.
As noted above, conventional solid state image sensing devices are accompanied by a problem of a smear phenomenon due to oblique incident lights or the like. Suppressing the smear phenomenon with the conventional methods produces other problems such as insufficient sensitivity and "white scratch" defects.